I've run into various problems with GWT over the past few years and the answer to my question is always "There's a reporting error" or "GWT data is made to be inaccurate". What's the point of using such a tool if it's so unreliable?
I think reliability here has to do with how quick you expect results and how large your site is. Google's robots deals with (I'm guessing here) billions of pages per day. If you have a large site and you just submitted a sitemap to GSC (new name for GWT) for indexing and you expect decent results within an hour, then you might not get what you wish for.
For instance, I ran across a problem where indexed pages dropped 90%, CTR dropped 30%, impressions dropped 80%, and keyword clicks dropped from about 300 to 3.
So have I but I don't think to that extent though. Its quite possible that your content is a duplicate of other content or google may have added a new algorithm and your website has been badly hit by it. You may want to visit the search analytics section of GSC to see what people want then talk about those keywords more often in your site to increase the CTR.
After having this checked out by various people I was told it wasn't an issue and that it was just a reporting bug and that data on GWT is often inaccurate anyway.
Go into GSC, then select your domain then select the gear icon, then "site settings". Select Limit Google's maximum crawl rate, and move the slider all the way to the right for a chance to get better data sooner.
It will tell you the number of seconds it will wait minimum between requesting any two pages on your site. If you move the slider all the way to the left, you can see the maximum waiting time in seconds. Take this value and multiply that by the grand total number of pages you allow google to access on your site for indexing/crawling, etc.
Let's say you moved the slider so the value is:
2.033 requests per second
0.492 seconds between requests
And assume your website has 1,000 pages total. Then you take 1000 and multiply by 0.492, and you'll get 492 seconds which is how long you can expect google to take to index everything. Wait this amount of time at the very minimum before claiming that data from GSC is incorrect. I'd even add an additional day for good measure.
I also notice that search analytic data is only available for up to the last three days as the end date.
Shouldn't Google be giving webmasters accurate data on the performance of their website?
You may want to access Google's page-speed insights where it measures the performance of your page right away. A better tool I recommend is at webpagetest.org.